Currently, a standard used in a wireless local area network (WLAN for short) is the Institute of Electrical and Electronics Engineers (IEEE for short) 802.11 series. The WLAN may include a plurality of basic service sets (BSS for short). Network nodes in a basic service set include an access point (AP for short) and a station (STA for short). Each basic service set may include one access point and a plurality of stations associated with the access point.
Wireless Fidelity (Wi-Fi for short) operates on an unlicensed frequency band. Specifications in the 802.11ax standard are an extension of those in the conventional 802.11 series. The 802.11ax standard stipulates that both an access point and a station need to contend for a channel to perform data transmission. That is, in the basic service set, the access point or the station can send a transmission frame only after successfully completing a backoff procedure.
An access point is used as an example of a single-user transmission mechanism. The access point expects to perform frame exchange transmission with a same station for a plurality of times in transmission opportunity (TXOP for short) duration. As shown in FIG. 1 (a), the access point performs backoff and obtains a channel through contention, and initially sends a downlink frame to the station in the transmission opportunity duration. After a short interframe space (SIFS for short, SIFS=16 μs), the station replies to the access point with an uplink frame. In this case, the access point successfully completes an initial frame exchange sequence. The access point determines that the access point holds a transmission opportunity in the transmission opportunity duration. As shown in FIG. 1 (b), if the access point fails the initial frame exchange sequence, the access point cannot hold a transmission opportunity in the transmission opportunity duration. In this case, the access point can send a downlink frame only after performing backoff again and obtaining a channel through contention.
In a dense-station scenario, the access point may perform multiuser-scheduling transmission, to improve system efficiency. However, currently, the standard defines only a transmission opportunity determining method for the single-user transmission mechanism, and does not define a transmission opportunity determining method for a multiuser transmission mechanism. There are a plurality of different stations in transmission opportunity duration in multiuser transmission. The plurality of different stations may have uplink/downlink data requirements of different service types. Therefore, the access point needs to perform uplink and/or downlink multiuser transmission with the plurality of different stations for a plurality of times. In this case, the transmission opportunity determining method for the single-user transmission mechanism is inapplicable to the multiuser transmission mechanism.